Radio communication system, method of operating a communication system, and a mobile station

ABSTRACT

In a mobile communication system comprising a base station ( 100 ) and a plurality of mobile stations ( 200 ) and operating closed loop transmitter power control, power control commands for transmission on an uplink are derived from measurements made on received downlink signals comprising non-predetermined data values. Optionally the non-predetermined data values may comprise power control commands for uplink transmit power control.

The present application is a continuation of U.S. application Ser. No. 10/554,376, filed on Nov. 16, 2006, which was the National Stage of International Application No. PCT/IB04/52347, filed on Nov. 9, 2004, which claims the priority of foreign application GB0326365.4 filed Nov. 12, 2003, each of which are incorporated by reference herein in their entirety.

The invention relates to a radio communication system, a method of operating a communication system, and a mobile station for use in a communication system.

In a radio communication system comprising base stations of fixed location and mobile stations, transmissions from a base station to a mobile station take place on a downlink channel and transmissions from a mobile station to a base station take place on an uplink channel. It is known to use downlink closed loop transmit power control in which a mobile station measures the quality of a received power controlled downlink pilot signal and transmits transmit power control (TPC) commands to a base station so that an adequate, but not excessive, received signal level is maintained at the mobile station despite fluctuations in downlink channel conditions. It is also known to use uplink closed loop transmit power control in which a base station measures the quality of a received uplink pilot signal and transmits transmit power control (TPC) commands to a mobile station so that an adequate, but not excessive, received signal level is maintained at the base station despite fluctuations in uplink channel conditions.

When a plurality of mobile stations share a channel, separate TPC commands are provided for each active mobile station because each mobile station will experience unique channel fluctuations. Similarly, a separate downlink pilot signal is provided for each active mobile station; each mobile station demodulates its respective pilot signal to estimate the channel characteristics prevailing for that mobile station and optionally to generate a phase reference. The estimated channel characteristics and the phase reference are then used to assist demodulating information carrying signals.

The pilot signals comprise predetermined data values to enable a mobile station readily to determine distortion introduced by the channel.

The pilot signals and the signals conveying the TPC commands are subject to transmit power control.

The transmission of the pilot signals and the TPC commands uses system resources. For example, in a Code Division Multiple Access (CDMA) system channel codes are required for the pilot signals and TPC commands, and in a Time Division Multiple Access (TDMA) system time slots are required for the pilot signals and TPC commands.

An object of the invention is to reduce the requirement for system resources.

According to a first aspect of the invention there is provided a mobile station for use in a communication system having a base station, the mobile station comprising:

-   receiver means for receiving from the base station a first downlink     signal, measurement means for measuring a parameter of the received     first downlink signal; -   power control means for generating first power control commands in     response to the measured parameter; and -   transmitter means for transmitting the first power control commands     to the base station; -   wherein the measurement means is adapted to measure the parameter of     the first downlink signal while first downlink signal is modulated     with non-predetermined data values and is subjected to transmit     power control in accordance with the first power control commands.

According to a second aspect of the invention there is provided a radio communication system comprising a base station and at least one mobile station in accordance with the first aspect of the invention.

According to a third aspect of the invention there is provided a method of operating a communication system comprising a base station and at least one mobile station, comprising at the base station, receiving first power control commands transmitted by the mobile station and transmitting a first downlink signal modulated with non-predetermined data values and subjected to transmit power control in accordance with the first power control commands, and at the mobile station, receiving the first downlink signal, measuring a parameter of the first downlink signal modulated with the non-predetermined data values, generating the first power control commands in response to the measured parameter, and transmitting the first power control commands.

The invention is based on the realization that downlink closed loop power control may be operated by measuring the quality of received downlink non-predetermined data symbols instead of predetermined pilot symbols, and that in some circumstances, separate downlink pilot signals for each active mobile station are not necessary for channel estimation. In some circumstances, downlink channel estimation is not required at all, and in other circumstances a common downlink pilot signal transmitted at a constant power level may be used instead of separate pilot signals. Consequently, operation is possible using fewer downlink system resources.

Optionally, the non-predetermined data values used for measuring the quality of a received signal for downlink closed loop power control may convey downlink TPC commands used for uplink power control.

The invention will now be described, by way of example only, with reference to the accompanying drawings wherein:

FIG. 1 is a block schematic diagram of a communication system; and

FIG. 2 is flow chart of a method of operating a communication system.

One application for the invention is in the Universal Mobile Telecommunication System (UMTS). In the UMTS Frequency Division Duplex (FDD) mode, in Release 5 of the UMTS Specifications which may be viewed at http://www.3gpp.org, it is possible to operate High Speed Downlink Packet Access (HSDPA) in such a way that a downlink dedicated channel is not needed for data (user or signaling), as data can be sent via the High Speed Downlink Shared Channel (HS-DSCH). A dedicated channel uses a single channel code for exactly one user, while a shared channel allows a plurality of users to share a single channel code, either simultaneously, or in rapid time multiplex. Even though data can be sent via a shared channel, a downlink Dedicated Channel (DCH) is still required for transmitting TPC commands for each active mobile station, in order to control the uplink transmit power.

The existence of a downlink DCH requires the allocation of a channel code for the duration of the connection. One way of operating the downlink DCH is to configure it as a fractional DCH which comprises only pilot symbols and TPC commands, with multiple users multiplexed on to the same channel code in such a way that each user uses the channel code for only a fraction of each timeslot. Signaling is used to assign mobile stations to use a particular channel code and fraction of a timeslot, in order to align the uplink and downlink power control timing. Such a scheme frees up channel codes which can be used to increase system capacity. However the present invention requires even fewer resources.

The requirement is for the mobile station to be able to derive a power control command to send in the uplink. This will then be used by the base station to adjust the power of the part of the fractional DCH corresponding to that mobile station.

The invention is based on the recognition that separate pilot symbols for each active mobile station are not necessary in at least two cases:

-   1) Where the transmitted phase of the DCH is referenced to that of a     common pilot signal, for example by using the same antenna(s) and     antenna weights for both the DCH and the common pilot signal to     which the phase of the DCH is referenced. In this case the     characteristics of the radio channel can be estimated from the     common pilot signal and this estimate can be used to demodulate the     TPC bits.

This first case is very likely to apply in HSDPA, as the HS-DSCH will be assigned a common pilot signal as a reference and the same common pilot signal can be used for the fractional DCH. Since the total power used by fractional DCH's is not likely to be very large, the benefits of separate antenna beamforming for fractional DCH will not be large.

-   2) Where different antennas or antenna weights are used for the     common pilot signal and the DCH, but the correlation between them is     sufficiently good that the common pilot signal can be used to make a     reasonable channel estimate for the DCH, such that the data on the     DCH can be received reliably.

So, in accordance with the invention the downlink fractional DCH can consist only of non-predetermined information bits multiplexed between users. A special case of particular interest is where these information bits carry TPC commands. The amplitude of individual TPC bits may be adjusted by the base station according to power control commands received from the—relevant mobile station. The mobile station determines the radio channel phase characteristics from an appropriate common pilot signal, demodulates the TPC commands, and increases or decreases the mobile station uplink DPCCH power as required. In addition, the mobile station uses the amplitude of the received TPC bits to determine any TPC commands sent in the uplink.

FIG. 1 is a block schematic diagram of a communication system comprising a base station 100 and a mobile station 200. In practice there would be a plurality of mobile stations 200, but for clarity only a single mobile station 200 is illustrated.

The mobile station 200 comprises a receiver 220 coupled to an antenna 210 for receiving radio signals transmitted by the base station 100. Coupled to an output of the receiver 220 is a measurement means 250 for measuring a parameter of a signal received from the base station 100. The measurement means 250 is adapted to measure the parameter of a signal which is modulated with non-predetermined data and is subjected to transmit power control by the base station 100. An output of the measurement means 250 is coupled to a first input of a power control means 230. The power control means 230 comprises a generation means (TPC 1) 232 for generating first TPC commands in response to the parameter measured by the measurement means 250. A first output of the power control means 230 is coupled to a first input 244 of a transmitter 240 for transmitting the first TPC commands via the antenna 210 to the base station 100.

The base station 100 comprises a transmitter 140 and a receiver 120 coupled to an antenna 110. The receiver 120 receives radio signals transmitted by the mobile station 200, in particular the first TPC commands. An input of a power controller (PC) 130 is coupled to an output of the receiver 120 for decoding the first TPC commands received from the mobile station 200, and a first output of the power controller 130 is coupled to a first input 142 of the transmitter 140 for controlling the transmit power of the transmitter 140 in accordance with the first TPC commands.

Optionally, at the base station 100, the power controller 130 measures the quality of a signal received from the mobile station 200 and, in response to the measured quality, generates second TPC commands. A second output of the power controller 130 is coupled to a second input 144 of the transmitter 140 for transmission of the second TPC commands to the mobile station 200, to control the transmit power of the mobile station 200.

Optionally, at the mobile station 200, the power control means 230 is coupled to an output of the receiver 220 and comprises a decoding means (TPC 2) 234 for decoding the second TPC commands. A second output of the power control means 230 is coupled to a second input 242 of the transmitter 240 for controlling the transmit power of the transmitter 240 in accordance with the second TPC commands. In this case, the non-predetermined data on which the measurement means 250 makes its measurement may be the second TPC commands.

Referring to FIG. 2, steps on the left hand side of the flow chart relate to steps performed at the base station 100, and steps on the right hand side of the flow chart relate to steps performed at the mobile station 200.

At step 310 the base station 100 receives first TPC commands from the mobile station 200.

At step 320 the base station 100 transmits to the mobile station 200 a signal modulated with non-predetermined data values and subjected to transmit power control in accordance with the first TPC commands.

At step 330 the mobile station 200 receives the signal modulated with the non-predetermined data values.

At step 340 the mobile station 200 measures a parameter of the signal modulated with the non-predetermined data values.

At step 350 the mobile station 200 generates the first TPC commands in response to the measured parameter.

Optionally, at step 360, the non-predetermined data values may comprise second TPC commands and the mobile station 200 may decode the second TPC commands, and at step 370 the mobile station may control its transmit power in accordance with the second TPC commands.

At step 380 the mobile station 200 transmits the first TPC commands generated at step 350.

Flow then reverts to step 310 and the process continues to loop. The signal parameter measured by the measurement means 250 of FIG. 1, and at step 340 of FIG. 2, may be, for example, any of: signal to noise ratio; signal to interference ratio; E_(b)/No (where E_(b) is energy per bit and Nb is noise density).

The decision threshold for TPC commands sent in the uplink can be determined by setting a particular error rate requirement for the TPC commands received in the downlink. This is in contrast to current practice which is to set a decision threshold in terms of the signal to noise ratio required to meet a predetermined performance target, for example a frame error rate of a data channel. One application for the invention is a fractional control channel in UMTS FDD (frequency division duplex) mode. With a spreading factor of 256 there are 10 symbols per slot. Therefore one slot can conveniently support either 2, 5 or 10 users with 5, 2 or 1 symbol per TPC command respectively.

In another application of the invention in UMTS the spreading factor would be 128, which would support the use of Space Time Transmit Diversity (STTD) applied to groups of two symbols. In this case, there are 20 symbols per slot, so 10 users can be supported while still maintaining the 2 symbols per TPC command which are required for the STTD encoding process.

Optionally, by avoiding the need to transmit a separate pilot signal for each user, the energy that would have been used to transmit the separate pilot signals may be redeployed by increasing the number of symbols used to transmit the TPC commands, thus improving the reliability of the TPC commands.

In the present specification and claims the word “a” or “an” preceding an element does not exclude the presence of a plurality of such elements. Further, the word “comprising” does not exclude the presence of other elements or steps than those listed.

From reading the present disclosure, other modifications will be apparent to persons skilled in the art. Such modifications may involve other features which are already known in the art of mobile communications and which may be used instead of or in addition to features already described herein. 

The invention claimed is:
 1. A mobile station for use in a communication system, the mobile station comprising: a receiver configured to receive, from a base station, a first downlink signal over a downlink fractional dedicated channel; a control circuit configured to: measure a parameter of the received first downlink signal; and generate first power control command in response to the measured parameter; and a transmitter configured to transmit the first power control command to the base station, the first power control command being configured to be utilized by the base station to control transmit power of a second downlink signal; wherein the control circuit is configured to measure the parameter of the first downlink signal while the first downlink signal is modulated with multiplexed non-predetermined data values, wherein the first downlink signal consists of the multiplexed non-predetermined data values, the fractional dedicated channel including a plurality of slots carrying a portion of the multiplexed non-predetermined data values, each slot of said plurality of slots being configured to communicate non-predetermined data values for a plurality of mobile stations in the communication system, and wherein the control circuit is further configured to decode non-predetermined data values comprising a second power control command from a slot of the plurality of slots and to adjust the transmit power of the transmitter in accordance with the decoded second power control command.
 2. The mobile station of claim 1, wherein the receiver is configured to receive from the base station a second, non-power controlled downlink signal and to derive a channel estimate from the second non-power controlled downlink signal, and to employ the channel estimate to decode the first downlink signal.
 3. The mobile station of claim 1, wherein the receiver is configured to receive a common downlink pilot signal from the base station, and wherein the control circuit configured to perform downlink channel estimation based on the received common pilot signal.
 4. The mobile station of claim 1, wherein a transmitted phase of the downlink fractional dedicated channel is referenced to a common pilot signal.
 5. The mobile station of claim 4, wherein different antennas or antenna weights are used for the common pilot signal and the downlink fractional dedicated channel.
 6. The mobile station of claim 1, wherein the power control circuit is configured to measure an error rate of the decoded second power control command, and wherein the transmitter is configured to send the first power control command when the measured error rate exceeds a predetermined threshold.
 7. A base station comprising: a transmitter configured to transmit, to a mobile station, a first downlink signal over a downlink fractional dedicated channel, the first downlink signal being modulated with multiplexed uplink power control commands, wherein the first downlink signal consists of the multiplexed uplink power control commands, the fractional dedicated channel including a plurality of slots carrying a portion of the multiplexed uplink power control commands, each slot of said plurality of slots being configured to communicate uplink power control commands for a plurality of mobile stations; a receiver configured to receive, from the mobile station, a downlink power control command; and a power control circuit configured to control transmit power of a second downlink signal based on the downlink power control command, wherein the power control circuit is configured to measure a quality of a signal received from the mobile station and generate the uplink power control command based on the measured quality.
 8. The base station of claim 7, wherein the transmitter is configured to transmit a common downlink pilot signal to the mobile station, and wherein the mobile station is configured to perform downlink channel estimation based on the common pilot signal.
 9. A method for communicating in a communication system, the method comprising: receiving, from a base station, a first downlink signal over a downlink fractional dedicated channel; measuring a parameter of the received first downlink signal while the first downlink signal is modulated with multiplexed non-predetermined data values, wherein the first downlink signal consists of the multiplexed non-predetermined data values, the fractional dedicated channel including a plurality of slots carrying a portion of the multiplexed non-predetermined data values, each slot of said plurality of slots being configured to communicate non-predetermined data values for a plurality of mobile stations in the communication system; generating a first power control command in response to the measured parameter; decoding non-predetermined data values comprising a second power control command; and transmitting the first power control command to the base station utilizing a transmit power that is based on the decoded second power control commands, wherein the first power control command is configured to be utilized by the base station to control transmit power of a second downlink signal.
 10. The method of claim 9, comprising receiving from the base station a second, non-power controlled downlink signal, deriving a channel estimate from the second non-power controlled downlink signal, and decoding the first downlink signal based on the derived channel estimate.
 11. A method for communicating in a communication system, the method comprising; receiving, from a mobile station, a downlink power control command; transmitting, to the mobile station, a first downlink signal that is modulated with multiplexed first uplink power control commands, wherein the first downlink signal consists of the multiplexed first uplink power control commands, the first downlink signal being transmitted over a downlink fractional dedicated channel that includes a plurality of slots carrying a portion of the multiplexed first uplink power control commands, each slot of said plurality of slots being configured to communicate first uplink power control commands for a plurality of mobile stations in the communication system, wherein a transmit power of the first downlink signal is controlled based on the downlink power control command, measuring a quality of a signal received from the mobile station; generating a second uplink power control command based on the measured quality; and transmitting the second uplink power control command to the mobile station.
 12. The method of claim 11, comprising transmitting a common downlink pilot signal to the mobile station, and wherein the mobile station is configured to perform downlink channel estimation based on the common pilot signal.
 13. A communication system comprising: a base station; and a plurality of mobile stations; the base station configured to: measure a quality of a signal received from each of the plurality of mobile stations; generate uplink power control commands based on the measured quality; encode the uplink power control commands as multiplexed non-predetermined data values; and transmit a first downlink signal consisting of the multiplexed non-predetermined data values to the plurality of mobile stations; and each mobile station of the plurality of mobile stations being configured to: receive, from the base station, the first downlink signal over a downlink fractional dedicated channel; measure a parameter of the received first downlink signal while the first downlink signal is modulated with the multiplexed non-predetermined data values, the fractional dedicated channel including a plurality of slots carrying a portion of the multiplexed non-predetermined data values, each slot of said plurality of slots being configured to communicate non-predetermined data values for a plurality of mobile stations in the communication system; generate downlink power control commands in response to the measured parameter; decode non-predetermined data values comprising the uplink power control command intended for the mobile station; and transmit the downlink power control command to the base station utilizing a transmit power that is based on the uplink power control command, wherein the base station is further configured to transmit a second downlink signal that is subjected to transmit power control based on the downlink power control commands from the plurality of mobile stations.
 14. The mobile station of claim 1, wherein the control circuit is further configured to decode a single slot out of said plurality of slots of the downlink fractional dedicated channel, said single slot of said plurality of slots being configured to communicate the non-predetermined data values dedicated for said mobile station.
 15. The mobile station of claim 1, wherein the control circuit is configured to decode uplink power control commands from a plurality of slots.
 16. The base station of claim 7, wherein the transmitter is further configured to encode a single slot out of said plurality of slots of the downlink fractional dedicated channel, said single slot of said plurality of slots being configured to communicate the non-predetermined data values dedicated for said mobile station.
 17. The method of claim 9, further comprising decoding a single slot out of said plurality of slots of the downlink fractional dedicated channel, said single slot of said plurality of slots being configured to communicate the non-predetermined data values dedicated for said mobile station.
 18. The method of claim 9, wherein decoding the non-predetermined data values comprises decoding the non-predetermined data values from a plurality of slots.
 19. The method of claim 11, further comprising encoding a single slot out of said plurality of slots of the downlink fractional dedicated channel, said single slot of said plurality of slots being configured to communicate the non-predetermined data values dedicated for said mobile station.
 20. The communication system of claim 13, wherein the mobile station is further configured to decode a single slot out of said plurality of slots of the downlink fractional dedicated channel, said single slot of said plurality of slots being configured to communicate the non-predetermined data values dedicated for said mobile station.
 21. The communication system of claim 19, wherein decoding the non-predetermined data values comprises decoding the non-predetermined data values from a plurality of slots.
 22. A mobile station for use in a communication system, the mobile station comprising: a receiver configured to receive, from a base station, a first downlink signal over a downlink fractional dedicated channel; control circuitry configured to: measure a parameter of the received first downlink signal; generate first power control commands in response to the measured parameter; and transmit the first power control commands to the base station using a transmitter, the first downlink signal being modulated with multiplexed non-predetermined data values, the first power control commands configured to be utilized to control transmit power of a second downlink signal, the first downlink signal consisting of the multiplexed non-predetermined data values; decode a single slot out of a plurality of slots of the downlink fractional dedicated channel, said single slot of said plurality of slots being configured to communicate non-predetermined data values dedicated for said mobile station, the non-predetermined data values comprising second power control commands; and adjust the transmit power of the transmitter in accordance with the second power control commands.
 23. The mobile station of claim 22, wherein the receiver is configured to receive from the base station a third non-power controlled downlink signal; and the circuitry is further configured to derive a channel estimate from the third non-power controlled downlink signal, and to employ the channel estimate to decode the first downlink signal.
 24. The mobile station of claim 22, wherein the receiver is configured to receive a common downlink pilot signal from the base station; and the circuitry is further configured to perform downlink channel estimation based on the received common pilot signal.
 25. The mobile station of claim 22, wherein a transmitted phase of the downlink fractional dedicated channel is referenced to a common pilot signal.
 26. The mobile station of claim 25, wherein different antennas or antenna weights are used for the common pilot signal and the downlink fractional dedicated channel.
 27. The mobile station of claim 22, wherein the control circuitry is further configured to measure an error rate of the second power control commands, and send the first power control commands, when the measured error rate exceeds a predetermined threshold.
 28. The mobile station of claim 22, wherein the downlink fractional dedicated channel includes said plurality of slots carrying a portion of the multiplexed non-predetermined data values, each slot of said plurality of slots being configured to communicate non-predetermined data values for a different respective mobile station in the communication system.
 29. A base station comprising; a transmitter; a receiver; control circuitry configured to: transmit, using the transmitter, a first downlink signal to a mobile station over a downlink fractional dedicated channel, the first downlink signal being modulated with multiplexed first uplink power control commands, wherein the first downlink signal consists of the multiplexed first uplink power control commands; encode a plurality of slots of the fractional dedicated channel, said plurality of slots including a single slot that is configured to carry a first uplink power control command dedicated for said mobile station; receive, via the receiver, downlink power control command from the mobile station; control transmit power of a second downlink signal based on the downlink power control command; measure a quality of a signal received from the mobile station; generate a second uplink power control command based on the measured quality; and transmit, using the transmitter, the second power control command to the mobile station.
 30. The base station of claim 29, wherein the circuitry is further configured to transmit, using the transmitter, a common downlink pilot signal to the mobile station so as to enable the mobile station to perform downlink channel estimation based on the common pilot signal.
 31. The base station of claim 29, wherein the fractional dedicated channel includes the plurality of slots carrying a portion of the multiplexed first uplink power control commands, each slot of said plurality of slots being configured to communicate a first uplink power control command for a different respective mobile station.
 32. A mobile station for use in a communication system, the mobile station comprising: a radio receiver configured to receive, from a base station, a first downlink signal over a downlink fractional dedicated channel, the first downlink signal configured to carry only multiplexed uplink transmit power control commands; a control circuit configured to: measure a parameter of the received first downlink signal; and generate a downlink transmit power control command in response to the measured parameter; and a radio transmitter configured to transmit the downlink transmit power control command to the base station, wherein the downlink transmit power control command is configured to be utilized by the base station to modulate a second downlink signal, wherein the control circuit is further configured to decode a single uplink power control command of the multiplexed uplink power control commands, and wherein the control circuit is configured to adjust the transmit power of the radio transmitter based on the decoded uplink power control command.
 33. The mobile station of claim 32, wherein the radio receiver is configured to receive a common downlink pilot signal from the base station; and the signal analyzing circuit is further configured to perform downlink channel estimation based on the received common pilot signal.
 34. The mobile station of claim 32, wherein a transmitted phase of the downlink fractional dedicated channel is referenced to a common pilot signal.
 35. The mobile station of claim 34, wherein different antennas or antenna weights are used for the common pilot signal and the downlink fractional dedicated channel.
 36. The mobile station of claim 32, wherein the signal analyzing circuit is further configured to measure an error rate of the uplink transmit power control commands, and send the downlink transmit power control commands, when the measured error rate exceeds a predetermined threshold.
 37. The mobile station of claim 32, wherein the downlink fractional dedicated channel includes said plurality of slots carrying a portion of the multiplexed non-predetermined data values, each slot of said plurality of slots being configured to communicate non-predetermined data values for a different respective mobile station in the communication system.
 38. A base station comprising; a radio transmitter; a radio receiver; control circuitry configured to: transmit, using the radio transmitter, a first downlink signal to a mobile station over a downlink fractional dedicated channel, the first downlink signal configured to carry only multiplexed uplink transmit power control commands, wherein the control circuitry is configured to measure a quality of a signal received from the mobile station and generate the uplink transmit power control commands based on the measured quality; and encode a plurality of slots of the fractional dedicated channel, said plurality of slots each including uplink transmit power control commands for a plurality of mobile stations; receive, via the radio receiver, downlink transmit power control commands from the mobile station; and control transmit power of a second downlink signal based on the downlink transmit power control commands.
 39. The base station of claim 38, wherein the control circuitry is further configured to transmit, using the radio transmitter, a common downlink pilot signal to the mobile station so as to enable the mobile station to perform downlink channel estimation based on the common pilot signal.
 40. The base station of claim 38, wherein the fractional dedicated channel includes the plurality of slots carrying the multiplexed uplink transmit power control commands, each slot of said plurality of slots being configured to communicate an uplink transmit power control command for a different mobile station. 